In recent years, high integration and high density in semiconductor device demands smaller and smaller wiring patterns or interconnections and also more and more interconnection layers. Multilayer interconnections in smaller circuits result in greater steps which reflect surface irregularities on lower interconnection layers. An increase in the number of interconnection layers makes film coating performance (step coverage) poor over stepped configurations of thin films. Therefore, better multilayer interconnections need to have the improved step coverage and proper surface planarization. Further, since the depth of focus of a photolithographic optical system is smaller with miniaturization of a photolithographic process, a surface of the semiconductor device needs to be planarized such that irregular steps on the surface of the semiconductor device will fall within the depth of focus.
Thus, in a manufacturing process of a semiconductor device, it increasingly becomes important to planarize a surface of the semiconductor device. One of the most important planarizing technologies is chemical mechanical polishing (CMP). In the chemical mechanical polishing, while a polishing liquid (slurry) containing abrasive particles such as silica (SiO2) or ceria (CeO2) therein is supplied onto a polishing pad, a substrate such as a semiconductor wafer is brought into sliding contact with the polishing pad and polished using the polishing apparatus.
CMP (Chemical Mechanical Polishing) apparatus is used in a process of polishing a surface of a substrate in a semiconductor device fabrication. The CMP apparatus is designed to hold and rotate the substrate by a top ring and press the substrate against a polishing pad on a rotating polishing table to polish the surface of the substrate. During polishing, a polishing liquid (slurry) is supplied onto the polishing pad, so that the surface of the substrate is planarized by a chemical action of the polishing liquid and a mechanical action of the abrasive particles contained in the polishing liquid.
A polishing rate of the substrate depends not only on a polishing load on the substrate against the polishing pad, but also on a surface temperature of the polishing pad. This is because the chemical action of the polishing liquid on the substrate depends on the temperature. Thus, it is important for the semiconductor device fabrication to maintain an optimum surface temperature of the polishing pad during polishing of the substrate in order to increase the polishing rate and keep the polishing rate constant.
Therefore, the present applicant has proposed in Japanese Laid-Open Patent Publication No. 2012-176449 a polishing apparatus which has a pad temperature adjustment mechanism for adjusting a surface temperature of a polishing pad by supplying a temperature-adjusted liquid to a pad contact member that is brought into contact with the surface of the polishing pad.
Because of special importance placed on an increase in the polishing rate, the pad contact member proposed in Japanese Laid-Open Patent Publication No. 2012-176449 is designed to have the largest possible contact area under layout restrictions in order to quickly raise the surface temperature of the polishing pad to a target temperature. Specifically, the pad contact member extends, in the radial direction of the polishing pad, from a peripheral position on the polishing pad to a position near the center of the polishing pad. In view of the expected radial temperature gradient of the surface of the polishing pad during polishing, the width of the pad contact member is large at an outer circumferential side of the polishing pad and is gradually smaller toward the center of the polishing pad. Thus, the pad contact member has a generally triangular planar-shape, and is a plate-like body having a liquid flow passage therein.
The present applicant has obtained the following knowledge through repetition of a process for polishing substrates by a polishing pad whose temperature has been raised by using a pad contact member as described in Japanese Laid-Open Patent Publication No. 2012-176449.
Since the pad contact member is designed to have the largest possible contact area under layout restrictions in order to quickly raise the surface temperature of the polishing pad with the emphasis on an increase of the polishing rate, the temperature of the polishing pad in its entirety can be raised quickly. However, temperature distribution of the polishing pad is such that the increase in the temperature is larger in the outer circumferential portion of the polishing pad than in the central portion of the polishing pad. Thus, it has been found that since the temperature of the polishing pad in its entirety can be raised by the pad contact member, the polishing rate is increased, but the polishing profile is deformed and become the concave. Thus, the central portion of the surface, being polished, of the substrate is polished more than the peripheral portion thereof, resulting in the concave central portion of the substrate. If the temperature of the polishing pad is not raised, the polishing profile is not deformed and does not become the concave. Thus, it has been found that the temperature distribution in the radial direction of the polishing pad and temperature history of the substrate which is experienced during polishing need to be approximated to those as observed in polishing performed without a pad contact member.